Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $87.88   5.749%   $92.9322   $92.93   $92.95   $92.90  
  Purchase #2 $8.45   3.450%   $8.7415   $8.74   $8.75   $8.70  
  Purchase #3 $27.51   3.734%   $28.5372   $28.54   $28.55   $28.50  
  Purchase #4 $69.81   8.377%   $75.658   $75.66   $75.65   $75.70  
  Purchase #5 $13.39   3.442%   $13.8509   $13.85   $13.85   $13.90  
  Purchase #6 $53.58   5.392%   $56.469   $56.47   $56.45   $56.50  
  Purchase #7 $9.40   11.800%   $10.5092   $10.51   $10.50   $10.50  
  7 purchase totals = $270.02       $286.6980   $286.70   $286.70   $286.70